1. Field of the Invention
The present invention relates to a reflection-type color liquid crystal display apparatus and a method for manufacturing the same. More particularly, the invention relates to a reflection-type color liquid crystal display apparatus and a method for manufacturing the same, wherein a color filter is provided on a substrate where a liquid crystal driving element is formed.
2. Description of the Related Art
As display apparatuses for various information apparatuses or the like, reflection-type color liquid crystal display apparatuses are widely used. FIG. 1 is a sectional view showing a structure of one example of a conventional reflection-type color liquid crystal display apparatus. The conventional reflection-type color liquid crystal display apparatus comprises, as shown in FIG. 1, a liquid crystal driving element formation substrate 101 on which a thin film transistor (TFT) serving as a switching element (a driving element) for driving a liquid crystal is formed, an opposite substrate 102 which is opposed to the substrate 101, and a liquid crystal 103 sandwiched between both the substrates 101 and 102.
The liquid crystal driving element formation substrate 101 comprises, as shown in FIG. 1, a transparent insulation substrate 104 made of glass or the like; a gate electrode 105 and a reflection plate 106 formed of aluminum, aluminum alloy or the like, which is formed on the transparent substrate 104; a gate insulation film 107 formed of silicon nitride or the like, which is formed on the gate electrode 105 and the reflection plate 106; a semiconductor layer 108 formed of an amorphous silicon or the like, which is formed on the gate insulation film 107 above the gate electrode 105; a drain electrode 109 and a source electrode 110 formed of chromium or the like, which are connected to both ends of the semiconductor layer 108, respectively; and an insulation protection film 111 formed of silicon nitride or the like, which covers the drain electrode 109, the semiconductor layer 108 and the source electrode 110. The gate electrode 105, the gate insulation film 107, the semiconductor layer 108, the drain electrode 109 and the source electrode 110 constitute the TFT.
Furthermore, the liquid crystal driving element formation substrate 101 comprises a black matrix 112 formed on the insulation protection film 111, for preventing the incidence of light into the TFT and shielding light at a portion which is not associated with display; a color filter 113 formed on the insulation protection film 111; an insulation protection film 114 made of acryl polymer or the like, which covers the black matrix 112 and the color filter 113; a contact hole 117 formed in the insulation protection film 111, the black matrix 112 and the insulation protection film 114 so as to reach the source electrode 110, a pixel electrode 115 formed of Indium Tin Oxide (ITO) which is formed on the insulation protection film 114 so as to be connected to the source electrode 110 via the contact hole 117; and a liquid crystal orientation layer 116 formed of polyimide or the like, which is formed on the pixel electrode 115.
Furthermore, the opposite substrate 102 comprises a transparent insulation substrate 121 formed of glass or the like; a common opposite electrode 122 formed of ITO or the like which is formed on the transparent insulation substrate 121; and a liquid crystal orientation layer 123 formed of polyimide or the like, which is formed on the opposite electrode 122.
According to the conventional reflection-type color liquid crystal display apparatus having the above structure, since the black matrix 112 and the color filter 113 are formed on the liquid crystal driving element formation substrate 101, an overlap margin is not required to be taken wherein a deviation of both the substrates 101 and 102 are considered in the case of assembling the reflection-type color liquid crystal display apparatus by sandwiching the liquid crystal 103 between the liquid crystal driving element formation substrate 101 and the opposite substrate 102, so that an opening ratio can be enlarged as compared with other structures in which the black matrix 112 and the color filter 113 are formed on the opposite substrate 102, and brighter display can be provided.
In the reflection-type color liquid crystal display apparatus having the structure described above, light scattering mechanism for scattering light incident from the side of the opposite substrate 102 is required especially when a white color is displayed.
For example, Japanese Patent Application Laid-Open No. hei 11-84415 discloses one example of a reflection-type color liquid crystal display apparatus which provides a white color display as described above. FIG. 2 is a sectional view showing a structure of another conventional reflection-type color liquid crystal display apparatus. As shown in FIG. 2, the another conventional reflection-type color liquid crystal display apparatus is constituted such that a light scattering plate 125 is provided outside of the transparent insulation substrate 121 of the opposite substrate 102. In other words, the another conventional reflection-type color liquid crystal display apparatus allows the light scattering plate 125 provided outside of a panel of the opposite substrate 102 to function as light scattering mechanism to provide a white color display. Except for the above, the constitution shown in FIG. 2 is approximately the same as that shown in FIG. 1, so that respective portions of FIG. 2 corresponding to those of the conventional reflection-type color liquid crystal display apparatus shown in FIG. 1 are denoted with same reference numerals, and an explanation thereof will be omitted here.
However, since the conventional reflection-type color liquid crystal display apparatus is provided with the light scattering mechanism outside of the opposite substrate, the starting point of scattering is set at a point distant from the liquid crystal so that the contrast is lowered.
FIGS. 3 and 4 are sectional views for schematically explaining the reason why the contrast is lowered in the conventional reflection-type color liquid crystal display apparatus. In the case where the scattering plate 125 serving as the light scattering mechanism is provided outside of the opposite substrate 102, light 131A, 131B, 131C, . . . 131N incident on a specific incident light region 130 from the outside are irregularly reflected at a boundary portion between the scattering plate 125 and the opposite substrate 102 to be spread in a radial configuration. Then, after part of the irregularly reflected light is incident on the end portion of a color filter 113, for example, a R(Red) color filter 113R of an R pixel through a liquid crystal 103R (Red), it is reflected by the reflection plate 106 to pass through a B(Blue) color filter 113B of a B(Blue) pixel which is adjacent to the R pixel and a liquid crystal 103B (Blue) of the B pixel adjacent to the R pixel, and the light is emitted as abnormal light 131X. Essentially, it is desired that, after the light incident on the color filter 113R of the R pixel is reflected by the reflection plate 106, the light passes only through the color filter 113R of the R pixel and liquid crystal 103R and it is emitted as normal light 131Z. As apparent from what has been described above, the specific incident light region 130 causes the generation of color mixing or uncontrollable light.
The fact that light passes through two color filters, like light 134 shown in FIG. 4, means that color mixing is generated. On a pixel region in which red color is to be essentially displayed, a mixture of red and blue colors is displayed. Furthermore, the light passes through the liquid crystals of the two pixel regions with the result that uncontrollable light 135, in which a phase difference cannot be predicted, is generated because the light passes through liquid crystals 103R and 103B and are controlled differently from each other. Consequently, the luminance of a black display will rise, even if the color Filter 113R of the R pixel attempts to provide a black display. Naturally, in the case where the light passes through both the color filter 113B and the liquid crystal 103B of the adjacent B pixels like light 136, both of the color mixing and uncontrollable light are simultaneously generated. The degree of such color mixing and the degree of the generation of uncontrollable light become large with an increase in light which traces the same path as the abnormal light 131X described above with the result that the hue reproduction zone is narrowed and the contrast is lowered. The lowering of the contrast becomes more remarkable as the starting point of scattering generated by the scattering plate 125, namely the position where the scattering plate 125 exists becomes distant from the liquid crystal 103.
Furthermore, as shown in FIG. 4, light 136 which passes through the liquid crystal 103R of the R(red) pixel region to enter into the color filter 113B of the adjacent B(blue) pixel and passes through the liquid crystal 103B of the blue pixel region to be emitted outside becomes different from light which the blue pixel essentially intends to display, thus leading to the lowering in the contrast. Consequently, even if the light does not pass through two color filters, the contrast is lowered only when the light passes through the portion of the liquid crystal 103 in the adjacent pixel region.
Furthermore, in the reflection-type color liquid crystal display apparatus having the conventional structure, the visibility of the emitted light is deteriorated. FIG. 5 is a sectional view schematically explaining the reason why the visibility is deteriorated in the conventional reflection-type color liquid crystal display apparatus.
In the case where an observer observes a view from a front surface position 132, light reflected by the reflection plate 106 to be emitted includes generation of light 137 which is directed in a slanting direction from the boundary of the pixel except for the light 133 which is directed to the front surface position 132 with the result that this light 137 is scattered with the scattering plate 125 and part of this light 137 becomes light 138 which is directed toward the front surface position 132.
Consequently, an observer comes to observe displayed image which is deviated by a distance between the light 133 and the light 138, so that the observer observes a blurred double image thereby deteriorating the visibility thereof.
An object of the present invention is to provide a reflection-type color liquid crystal display apparatus and a method for manufacturing the same, wherein contrast and visibility can be improved in a case where a white color is displayed by providing light scattering mechanism.
According to the present invention, there is provided a reflection-type color liquid crystal display apparatus where a liquid crystal is sandwiched between a liquid crystal driving element formation substrate and an opposite substrate. A color filter is provided on the liquid crystal driving element formation substrate. Light scattering mechanism is provided on the side of the liquid crystal of the opposite substrate.
The light scattering mechanism comprises, for example, an uneven portion formed at a surface of a transparent insulation substrate which constitutes the opposite substrate. Said surface where the uneven portion is formed, is positioned on the side of the liquid crystal.
Besides, the light scattering mechanism may comprise a flattened film formed to cover the uneven portion formed at the surface of the transparent insulation substrate.
Said light scattering mechanism may comprise an uneven insulation film formed on the surface of the liquid crystal side of the transparent insulation substrate.
In this case, the light scattering mechanism may comprise a scattering auxiliary film formed on the uneven insulation film, having a different refractive index from that of the uneven insulation film.
It is preferable that the refractive index of the uneven insulation film is larger than that of the scattering auxiliary film.
Besides, it is preferable that the light scattering mechanism may have a flattened film formed to cover the uneven insulation film.
Furthermore, the light scattering mechanism may have, for example, a flattened and scattering auxiliary film formed to cover the uneven insulation film.
According to the reflection-type color liquid crystal display apparatus of the present invention, the light scattering mechanism is provided on the side of the liquid crystal of the opposite substrate, so that the starting point of scattering in the opposite substrate is set to a point near to the liquid crystal. Thus, the generation of undesired light such as mixed color light, uncontrollable light or the like can be decreased.
The present invention provides a method for manufacturing a reflection-type color liquid crystal display apparatus in which a liquid crystal is sandwiched between a liquid crystal driving element formation substrate and an opposite substrate, and a color filter is provided on the liquid crystal driving element formation substrate. The method comprises the steps of: forming a liquid crystal driving element on a first transparent insulation substrate; then, forming at least a color filter on the first transparent insulation substrate to form a liquid crystal driving element formation substrate; providing a light scattering mechanism at a surface of a second transparent insulation substrate to form an opposite substrate; and sandwiching a liquid crystal between the liquid crystal driving element formation substrate and the opposite substrate by arranging the surface of the opposite substrate where the light scattering mechanism is provided is positioned on the side of the liquid crystal.
It is preferable that the light scattering mechanism comprises an uneven portion.
The uneven portion can be formed by a processing method including, for example, a sand blast method, or a photo-etching method.
In the method for manufacturing a reflection-type color liquid crystal display apparatus of the present invention, the light scattering mechanism can be provided with a simple method because the light scattering mechanism is constituted by forming the uneven portion on the side of the liquid crystal of the opposite substrate.
Consequently, in the case where the light scattering mechanism is provided to display a white color, contrast and visibility can be improved. dr
FIG. 1 is a sectional view showing a structure of one example of a conventional reflection-type color liquid crystal display apparatus.
FIG. 2 is a sectional view showing a structure of another conventional reflection-type color liquid crystal display apparatus.
FIG. 3 is a sectional view for schematically explaining a reason why contrast is lowered in the conventional reflection-type color liquid crystal display apparatus.
FIG. 4 is a sectional view for schematically explaining a reason why contrast is lowered in the conventional reflection-type color liquid crystal display apparatus.
FIG. 5 is a sectional view for schematically explaining a reason why visibility is lowered in the conventional reflection-type color liquid crystal display apparatus.
FIG. 6 is a plan view showing a structure of a reflection-type color liquid crystal display apparatus according to a first embodiment of the present invention.
FIG. 7 is a sectional view taken along line Axe2x80x94A of FIG. 6.
FIG. 8 is a sectional view for schematically explaining a reason why contrast is improved in the reflection-type color liquid crystal display apparatus according to the first embodiment.
FIG. 9 is a sectional view for schematically explaining a reason why visibility is improved in the reflection-type color liquid crystal display apparatus according to the first embodiment.
FIGS. 10A and 10B are sectional views showing a method for manufacturing a reflection-type color liquid crystal display apparatus according to the first embodiment in order of steps.
FIGS. 11A and 11B are sectional view showing the method for manufacturing the reflection-type color liquid crystal display apparatus according to the first embodiment of the next step of FIG. 10B in order of steps thereof.
FIG. 12 is a model view showing one example of a process method for forming the light scattering mechanism in the method for manufacturing the reflection-type color display apparatus according to the first embodiment.
FIG. 13 is a sectional view showing another example of the process method for forming the light scattering mechanism in the method for manufacturing the reflection-type color liquid crystal display apparatus according to the first embodiment.
FIG. 14 is a sectional view showing a structure of the reflection-type color liquid crystal display apparatus according to a second embodiment of the present invention.
FIG. 15 is a sectional view showing a structure of the reflection-type color liquid crystal display apparatus according to a third embodiment of the present invention.
FIG. 16 is a sectional view showing a structure of the reflection-type color liquid crystal display apparatus according to a fourth embodiment of the present invention.
FIG. 17 is a sectional view showing a structure of the reflection-type color liquid crystal display apparatus according to a fifth embodiment of the present invention.
FIG. 18 is a sectional view showing a structure of the reflection-type color liquid crystal display apparatus according to a sixth embodiment of the present invention.